Flame control in the momentum-dominated fluid dynamics region

ABSTRACT

A combustion system includes a fuel nozzle and first and second electrodes. An electric charge is applied to a flame supported by the nozzle via the first electrode. An electrical potential applied to an aerodynamic surface of the second electrode. The electrically charged flame reacts to the electrical potential according to the respective magnitudes and polarities of the charge applied to the flame and the electrical potential applied to the aerodynamic surface. Where the polarities are the same, the flame is repelled by the aerodynamic surface, and where the polarities are in opposition, the flame is pulled into contact with the aerodynamic surface by the electrodynamic attraction.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority benefit from U.S. ProvisionalPatent Application No. 61/792,169, entitled “FLAME CONTROL IN THEMOMENTUM-DOMINATED FLUID DYNAMICS REGION”, filed Mar. 15, 2013; which,to the extent not inconsistent with the disclosure herein, isincorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to combustion systems, and moreparticularly, to electrode arrangements that affect flame shape andposition.

BACKGROUND

Combustion systems are employed in a vast number of applications, inindustry and commerce, and in private homes. Tightening governmentregulations, increasing costs of fuel, and public opinion all contributeto a continual pressure to reduce emissions and improve efficiency ofsuch combustion systems.

SUMMARY

Methods and apparatuses for stabilizing a flame within a combustionvolume may operate in identifying specific zones of thermo-physicalflame characteristics, i.e., a region with buoyancy-dominated fluiddynamics, a region with momentum-dominated fluid dynamics, or a flameholding region.

According to an embodiment, a combustion system is provided, whichincludes a fuel nozzle and first and second electrodes. An electriccharge is applied to a flame supported by the nozzle via the firstelectrode. An electrical potential is applied to an aerodynamic surfaceof the second electrode. The electrically charged flame reacts to theelectrical potential according to the respective magnitudes andpolarities of the charge applied to the flame and the electricalpotential applied to the aerodynamic surface. Where the polarities arethe same, the flame is repelled by the aerodynamic surface, and wherethe polarities are in opposition, the flame is pulled into contact withthe aerodynamic surface by the attraction between the oppositepolarities.

According to an embodiment, a combustion system is provided, having afuel nozzle, a voltage supply, and first and second electrodes. Thefirst electrode is coupled to the voltage supply, and positioned andconfigured to apply an electric charge to a flame supported by the fuelnozzle. The second electrode includes an aerodynamic surface coupled tothe voltage supply and positioned adjacent to the fuel nozzle. Theaerodynamic surface has portions that vary in distance from alongitudinal axis of the fuel nozzle. The voltage supply is configuredto apply the electric to the flame via the first electrode, and to applyelectrical energy to the flame via the aerodynamic surface of the secondelectrode.

If a polarity of the electrical energy applied by the second electrodeis the same as a polarity of the charge applied to the flame, theaerodynamic surface repels the flame, such that a lateral bias isapplied to the flame away from the second electrode. Conversely, if thevalues have opposite polarities, the flame is attracted to the secondelectrode, such that the flame tends to be biased toward continuouscontact with the second electrode along the length of the aerodynamicsurface.

According to an embodiment, the fuel nozzle comprises the firstelectrode, such that the electric charge is applied to fuel as it exitsthe nozzle, and is subsequently passed to the flame as the fuel iscombusted.

According to an embodiment, a third electrode is provided, preferablypositioned opposite the second electrode, and coupled to the voltagesupply.

The third electrode can include an additional aerodynamic surface,positioned so that movement of the flame toward the aerodynamic surfaceof the second electrode moves the flame away from the additionalaerodynamic surface, and vice-versa. By selection of the polarities of avoltage applied to the second and third electrodes, relative to thepolarity of the charge applied to the flame, the flame can be made tomove toward one or the other aerodynamic surface, or, in some cases, tobroaden to contact both surface or narrow to avoid both surfaces.

According to an embodiment, the second electrode is positioned andconfigured to generate vortices in the flame. Because the secondelectrode can be made to attract the flame, it can be smaller thanconventional flame holders.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present disclosure are described by wayof example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. Unless indicated asrepresenting the background art, the figures represent aspects of thedisclosure.

FIG. 1 illustrates regions that may be identified in a flame within acombustion volume, according to an embodiment of present disclosure.

FIGS. 2-4 show schematic views of combustion systems, according torespective embodiments.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings, whichare not necessarily to scale or proportion, similar reference characterstypically identify similar components, unless context dictatesotherwise. The illustrative embodiments described in the detaileddescription and drawings are not intended to limit the scope of theclaims. Other embodiments and/or other changes can be made withoutdeparting from the spirit or scope of the present disclosure.

In many of the embodiments disclosed below, various electrodes aredescribed as being configured to apply a charge, an electricalpotential, or electrical energy to a flame. While these terms are notnormally synonymous, they are often used interchangeably, as there issignificant overlap in their respective meanings, and it is oftendifficult to distinguish between them, or to do one without doing theothers. For the purposes of the present disclosure and claims, they canbe construed as being synonymous, except where a term is more explicitlydefined.

Various burner systems are disclosed herein as embodiments. Manyelements are omitted from the embodiments described, particularly wheresuch elements are not necessary for an understanding of the principlesdisclosed. In practice, these and other embodiments typically includemore extensive combustion systems used in industry and commerce as partsof, for example, boilers, refineries, smelters, foundries, commercialand residential HVAC systems, etc.

FIG. 1 is a schematic diagram of a portion of a burner 100 including aburner nozzle 106 configured to emit a fuel stream 102 along alongitudinal axis A of the nozzle and to support a flame 104, accordingto various embodiments. Relative particle velocity within the flame 104is represented by arrows V, of lengths corresponding to relativevelocity. For the purposes of the present disclosure, a flame can bedivided into three general regions or portions. The first region R₁,closest to the nozzle 106, is a flame-holding region. Adjacent to, anddownstream from the flame holding region R₁ is the second region R₂, amomentum-dominated fluid dynamics region, and furthest downstream, thethird region R₃ is a buoyancy-dominated fluid dynamics region.

The term flame particle refers primarily to gaseous atoms and/ormolecules that comprise the fluid within a flame, as well as the smallsolid particles that may be entrained within the flame.

A flame front 108 of the flame is located in the flame holding regionR₁. As fuel flows from the nozzle 106 in a downstream direction in thefuel stream 102 the flame front 108 is continually moving upstream. Thevelocity of the fuel stream 102 is a function of a number of factors,including the geometry of the nozzle 106 and the pressure of the fuelwithin the nozzle 106. Meanwhile, the flame propagation rate, i.e., thespeed at which the flame front 108 moves upstream, depends upon factorsthat include the type of fuel, the amount of oxygen available, ambienttemperature, etc. When the flame propagation rate and the fuel streamvelocity are at equilibrium, the flame 104 remains substantiallystationary relative to the nozzle 106, and the flame is said to bestable. There are a number of structures and methods known in the art bywhich a stable flame can be obtained under many conditions and across awide range of fuel stream velocities. According to the embodimentsdisclosed hereafter, the flame 104 can be stabilized in accordance withany appropriate structure or method.

Within the momentum-dominated fluid dynamics region R₂ of the flame 104,the velocity and vector of flame particles within the flame 104 aresubstantially determined by the velocity and vector associated with thefuel stream 102. In this region, the velocity of the flame particles issufficiently high that other common factors, including buoyancy, havelittle influence on their vectors. However, as the flame particles movedownstream, they lose velocity, and the buoyancy of the flame 104,relative to the cooler and denser surrounding gases, tends to push theflame 104 upward. As the flame particles move further downstream andcontinue to lose velocity, the direction of movement is increasinglydominated by flame buoyancy.

The shape of the flame 104, and the relative dimensions of the threeregions R₁-R₃, can vary significantly, according to many factors. Forexample, in some cases, the buoyancy-dominated fluid dynamics region R₃is nonexistent, or very nearly so, as in, e.g., some welding torchflames. In these types of flames, the fuel is substantially consumedbefore the velocity has dropped to a level where buoyancy can exert asignificant influence. In other cases, the momentum-dominated fluiddynamics region R₂ is substantially nonexistent, as in, for example, thecase of a candle flame or other flame in which little or no velocity isimposed on the flame by the fuel, so that the velocity and vector of theflame particles are entirely controlled by other factors, includingbuoyancy.

As illustrated in the embodiments disclosed below, the inventors haverecognized that application of electrical energy to themomentum-dominated fluid dynamics region R₂ of a flame can have asurprisingly strong affect on various flame characteristics such asshape, position, breadth, etc., even in cases where flame particlevelocity is relatively high.

FIG. 2 shows a schematic view of a combustion system 200, according toan embodiment, including a first electrode 202, a second electrode 208,a voltage supply 204, and an actuator 206. The first electrode 202includes an aerodynamic surface 210 adjacent to the nozzle 106 in aposition corresponding to the second flame region R₂ of the flame 104.In the embodiment shown in FIG. 2, the aerodynamic surface 210 includesirregularities or convolutions. The voltage supply 204 is configured toapply a respective voltage potential to each of the first and secondelectrodes 202, 208.

According to an embodiment, the second electrode 208 applies anelectrical charge to the flame 104, which then reacts to the electricalpotential at the first electrode 202. For example, according to anembodiment, the second electrode 208 applies a charge having a positivepolarity to the flame 104. The first electrode 202, including theaerodynamic surface 210, is also held at a positive voltage potential,which is repellent to the positively charged flame 104. The repellingeffect of the voltage potential at the first electrode 202, or acombination of the aerodynamic effect and the electrical repulsion,applies a lateral bias to the flame 104 along the length of the portionof the aerodynamic surface 210 that faces the flame 104, in a directionaway from the first electrode 202. This bias repels hot gases associatedwith the flame 104 from the aerodynamic surface 210, thereby keeping theaerodynamic surface cool. Because the strength of the repelling bias isa function of distance, the shape of the flame 104 tends to conform tothe contours of the aerodynamic surface 210, as shown in FIG. 2,maintaining a relatively constant distance from the surface, in spite ofthe various contours.

Alternatively, the first electrode 202 is held at a negative voltagepotential (or at ground potential), which is attractive to thepositively charged flame 104. In this case, the electrical attraction,or a combination of the aerodynamic effect and the electricalattraction, applies a lateral bias toward the first electrode 202,drawing the flame 104 into or toward continuous contact with theaerodynamic surface 210. This serves to increase heat transfer from theflame 104 to the aerodynamic surface 210. Of course, in otherembodiments, the polarities can be reversed from those described above.

In practice, the effect described can be employed in combustion systemsin which the combustion volume is defined in part by irregular surfaces.The electrical energy and polarity applied to the flame 104 and thesurfaces can be selected to either reduce or increase thermal couplingbetween the flame 104 and the surfaces in question, according to therequirements of the particular system. In conventional combustionsystems, where a heat transfer surface includes convolutions orirregularities, a flame may transfer heat most efficiently at the highspots of the surface, i.e., those portions that are closest to thelongitudinal axis A of the nozzle 106, while transferring relativelylittle heat at portions of the surface that are farthest from thelongitudinal axis A. In contrast, by appropriate selection of voltageand polarity, the flame 104 can be made to transfer heat substantiallycontinuously along a length of the surface, thereby reducing hot spotswhile increasing overall efficiency.

According to an alternate embodiment, the nozzle 106 (or a portionthereof) is electrically coupled to the voltage supply 204, as shown inphantom lines in FIG. 2, and is configured to act as a second electrode212 in place of the second electrode 208. In this embodiment, anelectric charge is applied to the fuel as it exits the nozzle 106, whereafter the flame 104 retains the charge and reacts with the firstelectrode 202 as previously described.

According to a further embodiment, the nozzle 106 is electricallycoupled to the voltage supply 204 as a third electrode 212, and isconfigured to apply a charge to the flame 104, while the first andsecond electrodes 202, 208 are configured to be held at respectivevoltage potentials and polarities in order to interact with the chargeapplied via the nozzle 106. For example, the second electrode 208 caninclude a second aerodynamic surface, so that the flame 104 passesbetween two such surfaces. By selection of the voltage and polarityapplied to each of the three electrodes 202, 208, 212, the flame 104 canbe made to selectively couple with only one of the two surfaces, withboth surfaces, or with neither surface.

Furthermore, according to an embodiment, a reactive moiety can beinstantaneously withdrawn or supplied to the combustion reaction in themomentum-dominated fluid dynamics region R₂. Withdrawing of electronsfrom the combustion reaction may enable parsing of more sub-formationsand may cause at least a temporary inability of reactants to react tocompletion within the combustion reaction. This may cause a temporaryformation of soot within the flame 104, which in turn can increaseradiation heat transfer from the flame 104 as soot particles are heatedto become incandescent.

The aerodynamic surface 210 can be a single surface or a plurality ofaerodynamic structures such as a turbine blade, a piece of refractorybrick, or any type of bluff body, amongst others, which can operate incombination with the application of electrical energy in the proximityof the resulting aerodynamic effect. The aerodynamic structures can bemade of high temperature-stable conductive materials, such as, e.g.,very high melting point metal or metal alloy, such as titanium or one ofa plurality of iron-nickel-cobalt super alloys, composite ceramicmaterials, etc., that is capable of sustaining high temperature flameswithout degradation or failure.

According to an embodiment, the aerodynamic surface 210 is a stationarystructure, relative to the nozzle 106. According to another embodiment,the aerodynamic surface 210 is part of a structure that moves or rotateswith respect to the longitudinal axis A of the nozzle 106. Movement ofthe aerodynamic surface 210 can be in any appropriate direction, suchas, e.g., parallel to the longitudinal axis A, transverse to the axis A,or a combination of both. Movement of the aerodynamic surface 210,relative to the longitudinal axis A, can be in translation, inorientation or both. In embodiments in which the aerodynamic surface 210is configured to move or rotate, appropriate mechanisms, such as theactuator 206, for example, are provided to enable the desired movement.

According to an embodiment, movement of the aerodynamic surface 210 iscoordinated with a modulation of a voltage applied to one or more of theelectrodes 202, 208, in order to create a spinning effect or otherpattern in the flame 104.

The application of combined aerodynamic and electrical effects inmomentum-dominated fluid dynamics region R₂ to increase or decrease heattransfer from the flame 104 to the aerodynamic surface 210 may affectthe chemistry of the flame 104, such that, for example, the flame 104 iseither transparent and non-incandescent, or incandescent yellow, in theform of hot black body radiator flames. This effect can be exploited toincrease or decrease output of infrared energy, as radiated energy, toradiation collection surfaces of combustion systems.

FIG. 3 is a schematic view of a combustion system 300, according to anembodiment, including a rotating first electrode 302 having aerodynamicsurfaces positioned adjacent to the momentum-dominated fluid dynamicsregion R₂ of flame 104. The rotating aerodynamic surfaces can be incontact or in proximity to the flame 104. The first electrode 302 isconfigured such that an aerodynamic effect causes the flame 104 to flowover the aerodynamic surfaces. Subsequently, a charge or an electricfield can be applied via the voltage supply 204 and the first and secondelectrodes 302, 208 to the momentum-dominated fluid dynamics region R₂to affect the flame 104. As previously described, an opposite polarityvoltage or a circuit ground potential can be applied to the firstelectrode 302 to bring flame 104 into closer contact with theaerodynamic surfaces, in order to extract higher heat transfer from theflame. Conversely, application of a same-polarity potential to the firstelectrode 302 can be employed to reduce the degree of contact and thecorresponding thermal coupling of the flame 104 with the aerodynamicsurfaces.

FIG. 4 depicts an embodiment of a combustion system 400, including anelectrode 208 and an aerodynamic surface 402 configured to operate incombination with the application of electrical energy in themomentum-dominated fluid dynamics region R₂. According to an embodiment,the aerodynamic surface 402 causes an interruption in the flame 104thereby causing vortices 404 to form on the leeward side of theaerodynamic surface 402 to maintain ignition of flame 104. When theaerodynamic effect is combined with an electrical effect created by theapplication of an opposite-polarity voltage to the aerodynamic surface402, a smaller aerodynamic structure can be used, thereby reducing theaerodynamic drag and maintaining lower back-pressure on flame 104, thusproducing an improved response of flame 104.

The aerodynamic surface 402 may be comprised, in part, of a refractorybrick which may be laterally introduced part way into the flame 104, asshown in FIG. 4, to form vortex 404 on the leeward side of theaerodynamic surface 402. A smaller aerodynamic surface 402, incombination with the application of electrical energy, as previouslydescribed, may be more effective in creating vortices 404 whilecontrolling the level of aerodynamic drag.

According to an embodiment, the voltage supply 204 is configured toapply an electric charge having a first polarity to the flame 104 via,for example, the electrode 208. The voltage supply is further configuredto apply a voltage potential having a second polarity opposite the firstpolarity at the leeward side of the aerodynamic surface 402, but notnecessarily on the entire aerodynamic surface 402, in order to providean attractive force to bring flame 104 into contact with the leewardside of the aerodynamic surface 402, increasing the tendency of theflame 104 and vortex 404 to remain intact. Therefore, by adding theelectric potential to the aerodynamic surface 402, the size of theprotuberance of the aerodynamic surface necessary to hold the flame 104can be reduced. This combination, in turn, reduces aerodynamic drag,resulting in a lower back-pressure on flame 104. In contrast,controlling the flame 104 with a conventional aerodynamic surface 402,alone, typically requires larger aerodynamic pressures under conditionsthat can cause high aerodynamic drag and a larger back-pressure level onflame 104.

According to an embodiment, the aerodynamic surface 402 is positionedand configured such that if the voltage potential applied to theaerodynamic surface 402 has the same polarity as the charge applied tothe flame 104, the flame will be repelled from the aerodynamic surface402 such that the flame 104 flows smoothly past the aerodynamic surface402 without obstruction. On the other hand, if the voltage potentialapplied to the aerodynamic surface 402 has the opposite polarity, theflame 104 is pulled into contact with the aerodynamic surface 402, andvortices 404 are generated. By selection and control of the relativemagnitudes and polarities of the voltage potential applied to theaerodynamic surface 402 and the charge applied to the flame 104, thedegree of contact between the flame 104 and the aerodynamic surface 402can be regulated. This feature may be advantageous in systems in whichfactors that affect the velocity of the fuel stream 102, and/or thepropagation rate of the flame front 108 vary during normal operation.

In another embodiment, the aerodynamic surface 402 includes an embeddedelectrode 410 to which an electric charge can be applied. Theaerodynamic surface 402 and the embedded electrode 410 act on an upwardflowing region of the flame 104 so that when a voltage having anopposite polarity (relative to the polarity of electric charges in theflame 104) is applied, flame 104 is attracted toward the electrode 410further adding to the formation of vortices 404 in themomentum-dominated fluid dynamics region R₂ of flame 104.

In a further embodiment, a reactive moiety is withdrawn or supplied tothe flame 104, in the momentum-dominated fluid dynamics region R₂. Whenelectrons are withdrawn from the combustion reaction at periods within arange of about 5 msec, for example, more sub-formations are temporarilyparsed causing temporary formation of soot that disrupts the ability ofthe reactants in the flame to react to completion. Subsequently, newlyformed soot is heated to incandescence and thereby increases theradiation heat transfer from the flame 104.

The aerodynamic surface 402 can be a cooled surface or made from a hightemperature stable material combined with the electrode 410. Theelectrode 410 can also be made from high temperature stable material.For relatively low adiabatic flame temperatures, metal alloy materialsthat do not degrade or fail under high temperature conditions can beemployed. A high temperature flame 104 may exceed the softening point ofa metal alloy. For these applications, ceramic materials can be used inspite of tensile strains that may be exhibited by composite ceramic.

Ordinal numbers, e.g., first, second, third, etc., are used in theclaims according to conventional claim practice, i.e., for the purposeof clearly distinguishing between claimed elements or features thereof.The use of such numbers does not suggest any other relationship, e.g.,order of operation or relative position of such elements. Furthermore,ordinal numbers used in the claims have no specific correspondence tothose used in the specification to refer to elements of disclosedembodiments on which those claims read, nor to numbers used in unrelatedclaims to designate similar elements or features.

The abstract of the present disclosure is provided as a brief outline ofsome of the principles of the invention according to one embodiment, andis not intended as a complete or definitive description of anyembodiment thereof, nor should it be relied upon to define terms used inthe specification or claims. The abstract does not limit the scope ofthe claims.

While various aspects and embodiments have been disclosed, other aspectsand embodiments may be contemplated. The various aspects and embodimentsdisclosed here are for purposes of illustration and are not intended tobe limiting, with the true scope and spirit being indicated by thefollowing claims.

What is claimed is:
 1. A combustion system, comprising: a fuel nozzle; avoltage supply; a first electrode coupled to the voltage supply,positioned and configured to apply an electric charge to a flamesupported by the fuel nozzle; and an aerodynamic surface coupled to thevoltage supply, positioned adjacent to the fuel nozzle and havingportions that vary in distance from a longitudinal axis of the fuelnozzle.
 2. The system of claim 1, wherein the fuel nozzle comprises thefirst electrode.
 3. The system of claim 1, wherein the voltage supply isconfigured to apply the electric charge having a first value to theflame via the first electrode, and to apply electrical energy having asecond value to the flame via the aerodynamic surface.
 4. The system ofclaim 3, wherein the first value and the second value are at a samepolarity.
 5. The system of claim 3, wherein the first value and thesecond value are at opposite polarities.
 6. The system of claim 3,wherein one of the first and second values is a ground potential.
 7. Thesystem of claim 3, wherein the voltage supply is configured toselectively control polarities of the first and second values.
 8. Thesystem of claim 3, comprising a second electrode coupled to the voltagesupply, positioned and configured to apply electrical energy to theflame supported by the nozzle.
 9. The system of claim 8, wherein thevoltage supply is configured to apply electrical energy having a thirdvalue to the flame via the second electrode.
 10. The system of claim 9,wherein the voltage supply is configured to apply the electric chargehaving the first value to the flame via the first electrode, and toselectively control polarities of the second and third values accordingto an intended effect on the flame.
 11. The system of claim 8, whereinthe second electrode includes an additional aerodynamic surface.
 12. Thesystem of claim 11, wherein the additional aerodynamic surface includesportions that vary in distance from the longitudinal axis of the fuelnozzle.
 13. The system of claim 3, wherein the aerodynamic surface ispositioned and configured such that when polarities of the first andsecond values are opposite each other, formation of vortices directlyupstream from the aerodynamic surface increases, relative to formationof vortices when the polarities of the first and second values are notopposite each other.
 14. The system of claim 1, wherein the aerodynamicsurface comprises a plurality of convolutions that include the portionsthat vary in distance from the longitudinal axis of the fuel nozzle. 15.The system of claim 1, wherein the aerodynamic surface is movablerelative to the longitudinal axis of the nozzle.
 16. The system of claim15, wherein the aerodynamic surface is translatable relative to thelongitudinal axis of the nozzle.
 17. The system of claim 15, wherein theaerodynamic surface is rotatable relative to the longitudinal axis ofthe nozzle.
 18. The system of claim 15, wherein the aerodynamic surfaceis one of a plurality of aerodynamic surfaces that are mechanically andelectrically coupled together and configured to rotate about a commonaxis.
 19. A method for controlling a flame, comprising: supporting aflame in a combustion volume; applying an electrical charge to theflame; applying a lateral bias to the flame along a length of anaerodynamic surface positioned adjacent to the flame by applying anelectrical potential to the aerodynamic surface.
 20. The method of claim19, wherein the applying a lateral bias to the flame includes applying alateral bias to the flame toward the aerodynamic surface by applying anelectrical potential having an opposite polarity from a polarity of theelectrical charge.
 21. The method of claim 19, wherein the applying alateral bias to the flame includes applying a lateral bias to the flameaway from the aerodynamic surface by applying an electrical potentialhaving a same polarity as a polarity of the electrical charge.
 22. Themethod of claim 19, wherein the applying a lateral bias to the flameincludes applying the lateral bias to the flame substantially within amomentum-dominated fluid dynamics region of the flame.
 23. The method ofclaim 19, comprising varying a value of the electrical potential. 24.The method of claim 19, comprising varying a polarity of the electricalpotential, relative to a polarity of the electrical charge.
 25. Themethod of claim 19, wherein the applying an electrical potentialcomprises applying a ground potential to the aerodynamic surface. 26.The method of claim 19, comprising increasing formation of vorticesdownstream from the aerodynamic surface, wherein the increasingformation of vortices includes the applying a lateral bias to the flame.27. The method of claim 19, wherein the supporting a flame includesemitting a fuel flow from a nozzle, the method further comprising movingthe aerodynamic surface relative to a longitudinal axis of the nozzle.